US 2010/0264746 A1 describes a wireless power transmitting system that transmits power from a radio-power-supply device to a radio-power receiving device wirelessly. The radio-power receiving device includes a unit receiving power from the radio-power-supply device, a unit obtaining a level of power received through the antenna, a unit obtaining a level of power consumed by the device operating while being supplied with received power and a unit transmitting the received power level and the power consuming level to the radio-power-supply device wirelessly. The radio-power-supply device includes a unit receiving the received power level and the power consuming level from the radio-power receiving device wirelessly, a unit controlling the level of power transmitted through the transmitting antenna based on the difference between the received power level and the received power consuming level, and a unit transmitting power to the radio-power receiving device wirelessly.